1. Field of the Invention
The present invention relates generally to the art of vehicle suspension systems and more particularly to suspension systems of the type which lower the vehicle when the vehicle is at rest or is operated below preset parameters but which elevate the vehicle when the vehicle is operated above said preselected parameters.
2. Description of the Prior Art
While the principles of the present invention are applicable to many kinds of vehicles, certain aspects of the prior art will be discussed in the context of the motorycycle art. Following such discussion, several patents will be described which relate to adjustable suspension systems for other types of vehicles, such as railroad cars and automobiles.
A typical motorcycle has a seat for the rider, the design height of which is determined principally to provide leg comfort for the rider. A hinged footrest is also provided. On the one hand, the footrest must be sufficiently low with respect to the seat for rider comfort, but, at the same time, it must be high enough to clear the ground during cornering of the bike. The compromise which has been adopted by the motorcycle industry has been to use a higher seat height. That compromise has resulted in compromises of other important design criteria; the motorcycles are more difficult to board and are harder to balance at rest and at slow operating speeds when the seat height is raised to provide leg comfort.
Another consideration involved in motorcycle design is the width of chassis components. Even if it is preferable for certain reasons to make certain components wider, the width typically must be kept at a standard width or reduced therefrom if they are low on the bike so that the desired ground clearance can be maintained. The problem is so significant that various engine configurations, many of which offer substantial other benefits, have been largely ignored for this reason.
Compromises have been made using low seat heights and high or forward mounted footrests, but motorcycles embodying such features provide an awkward and uncomfortable ride, especially on longer trips.
Suspension travel is another significant aspect of motorcycle design. A long suspension travel provides a significant improvement in ride quality. However, it has been difficult to provide long suspension travel in street motorcycles, due to the aforementioned problems with seat height and ground clearance.
There is yet another problem which arises if the overall cycle height is increased because of clearance or seat height considerations, i.e. the capsize mode or non-oscillatory tip-over tendency which exists at rest or slow operating speeds becomes more difficult for the operator to control. At typical road speeds, the gyroscopic effect of the wheels will stabilize a taller vehicle.
A vehicle suspension system which would allow a low seat height at rest, at low speeds or during certain deceleration modes, but which would provide necessary ground clearance and suspension travel at road speeds and during certain acceleration modes for various loading conditions would represent a significant advance in this art.
Adjustable vehicle suspensions are known in the prior art, especially for such vehicles as automobiles and railroad cars. Resort to such prior art, however, does not provide solutions to the above noted problems. A summary of several prior art patents will illustrate the different approaches which have been used and the different problems which such patents are attempting to overcome.
Frick et al., in U.S. Pat. No. 3,027,176 issued Mar. 27, 1962 for "Leveling Apparatus For Fluid Suspension Systems," disclose a system for preventing rapid fluctuation in suspension fluid pressure while a car is in motion but which allows rapid fluctuations when the vehicle is stopped or is being operated at slow speeds. The system is designed to prevent deterioration of handling characteristics as a vehicle corners, for example, in an S-shaped curve. Frick et al. employ a first vehicle speed responsive flow rate control valve located in the fluid line to the air springs. A second speed responsive flow control valve is located in the discharge line of the air springs, and a pressure pump is connected to the drive shaft of the vehicle which is responsive to changes in vehicle speed. When the vehicle is at rest, the pump is inactive and the valves allow an unrestricted flow through the fluid valves. In this condition, air can rapidly move in and out of the lines to permit rapid leveling of the vehicle in response to changes in vehicle loading due to passenger weight shifts or other weight changes. When the vehicle is accelerated, the pump develops pressure which in turn restricts fluid flow so that only sway changes lasting several seconds or more will substantially affect body support. Frick et al. is primarily directed to automobile support systems and is not applicable to the resolution of the motorcycle problems mentioned above. In fact, the concept is virtually the opposite of what is required to solve such motorcycle problems because preload is added in Frick et al. to compensate for extra loading at rest, while an ideal solution to the above-mentioned problems would remove the suspension preload at rest.
Systems are also known which compensate for vehicle load if the vehicle is travelling through a curved path. One such system is described in U.S. Pat. No. 3,572,747 issued to Pollinger et al. on Mar. 30, 1971 for "Air Suspension System For Vehicles." A compressor is used in this patent and is driven by a speed responsive clutch so that it only operates when the vehicle travels above a preselected speed. Level regulators are also provided which regulate suspension pressure depending on whether the vehicle is moving in a straight path or whether there is a sensed difference in the height of the longitudinal tilt axis of the vehicle. Pollinger et al. is also directed to automotive type vehicles.
Pollinger et al., in their U.S. Pat. No. 3,738,680 issued June 12, 1973 for "Pneumatic Suspension System for Vehicles" describe a bellows system used with railroad vehicles. The system switches from a four point to a three point suspension system when the vehicle is at rest or is operating at lower speeds. In the preferred embodiment of this patent, the change takes place when the pneumatic door closing device of the railroad car is actuated.
Hill et al., in their U.S. Pat. No. 3,603,612 issued Sept. 7, 1971 for "Suspension Systems For Road Vehicles" disclose a suspension in which dampening characterists are increased above a predetermined vehicle speed. Vehicle height is not adjusted when the vehicle is at rest.
Palazzetti discloses another suspension system in U.S. Pat. No. 3,770,292 issued Nov. 6, 1973 for "Electronic Control For Vehicle Suspension Systems." Suspension stiffness is varied with increasing and decreasing speed. Transverse acceleration is also compensated for, as are the transient vertical forces acting on the wheels due to unevenness of the road surface. Vehicle ride height is not altered at different speeds.
Another self-leveling vehicle suspension system is disclosed in Hiruma's U.S. Pat. No. 3,992,039 issued Nov. 16, 1976 for "Self-Levelling Vehicle Suspension System." This system compensates for pitch forward and in the rearward direction during acceleration or deceleration of the vehicle by restraint on a stabilizer bar. The control unit coupled to the bar is arranged to operate in a hydromechanical, electromechanical or hydroelectrical mode responsive to acceleration or deceleration.
Finally, several prior art patents disclose systems which allow the operator to lower the vehicle while it is at rest. For example, Fujii discloses a "Hydropneumatic Suspension System" in U.S. Pat. No. 4,212,484 issued July 15, 1980. The system lowers the level of the automobile, limousine or van to afford entry/exit and loading/unloading ease. A solenoid valve cuts the supply of fluid to self-leveling suspension units while inlets of the units are coupled to a reservoir by way of a relief valve. Other systems of this type include Bothwell's U.S. Pat. No. 3,314,685 issued Apr. 18, 1967 for "Low-Loading Road Vehicle" and Nallinger et al. U.S. Pat. No. 3,218,088 issued Nov. 16, 1965 for "Arrangement To Facilitate The Accessibility Of A Passenger Motor Vehicle." In the latter, the vehicle is raised to facilitate entry/exit, and the former relates to unique problems associated with ambulance loading and unloading, the chassis in Bothwell being lowered to the ground to permit loading of an injured person. None of these latter three patents disclose a speed-controlled automatic suspension lowering system which lowers the vehicle when it is at rest or is being operated below a certain speed and raises the vehicle above such speed.
A motorcycle suspension system is disclosed in Kawamura's U.S. Pat. No. 4,422,661 issued Dec. 27, 1983 for "Height Adjusting System for Motorcycles." This system uses an air pump driven by an electric motor which is activated by current flowing through a movable contact on the speedometer needle and a first fixed contact strip which covers the range from a predetermined low speed to the maximum speedometer speed. The air pump fills a high pressure tank which is then connected by air lines to electromagnetic valves which allow pressure to be provided to front and rear air suspension components. When each suspension pressure reaches its respective predetermined value, a pressure switch activates a solenoid which closes its respective valve and stops supplying current to the pump. Therefore, when both predetermined pressures have been reached, the pump is shut off and the filling valves are closed. When the speedometer needle indicates a speed at or below the predetermined speed, the movable contact passes current through a second fixed contact strip. This current opens exhaust valves which release the air from the suspension, thereby lowering the vehicle.
This system suffers from a number of design shortcomings. Current to run a pump of sufficient output to raise the vehicle in a short time is approximately 10 amperes at 12 volts. This current flow would cause significant problems with the sliding contact switching method described in this patent, unless the speedometer assembly was sealed and evacuated. Maintaining sufficient pressure to avoid contact opening due to vibration and road shock would affect speedometer response, and would cause wear. Another problem with the system is the lack of compensation for changes in vehicle loading, as different loads require different suspension pressures to maintain the correct ride height. A further problem is the use of a high pressure tank, which requires additional air volume, and increases the time required to fill the system and raise the vehicle. This tank may have been added to make use of a small pump requiring minimal current. In repeated stop and go use of the vehicle, as in use in city traffic, the tank would be depleted, and would even more significantly delay the raising of the vehicle.
Yet another problem with the patented system is a lack of any disarming system for the pump and valves. As the vehicle crosses large road irregularities the pressure in the suspension rises and falls. This system would, therefore, add pressure each time the suspension was unweighted, until the predetermined pressure was achieved at full suspension extension. This would raise the vehicle excessively, and increase the suspension rate beyond what is desirable. An additional problem with the aforesaid system is the lack of a dryer for the air. The large quantities of air required by this type of system would require a dryer of significant size and/or sophistication. Moreover, there is no signal for the vehicle operator to indicate that the vehicle is in the lower position. This would be required for safe operation of the vehicle in case of an air leak or pump failure.